A Hamiltonian circuit in a graph is a closed path that visits every vertex in the graph exactly once. (Such a closed loop must be a cycle.) A Hamiltonian circuit ends up at the vertex from where it started.
Hamiltonian Graph: If a graph has a Hamiltonian circuit, then the graph is called a Hamiltonian graph.
$\text{G1, G2, G3, G4}$ all are hamiltonian graphs.
